Organic electroluminescent device (OED) arrays are emerging as a potentially viable design choice for use in small products, especially small portable electronic devices, such as pagers, cellular and portable telephones, two-way radios, data banks, etc. OED arrays are capable of generating sufficient light for use in displays under a variety of ambient light conditions (from little or no ambient light to bright ambient light). Further, individual OEDs and arrays of OEDs can be fabricated relatively cheaply and in a variety of sizes from very small (less than a tenth millimeter in diameter) to relatively large (greater than an inch). Also, OEDs have the added advantage that their emissive operation provides a very wide viewing angle and they are relatively bright.
Generally, OEDs include a first electrically conductive layer (or first contact), an electron transporting, a hole transporting layer and a second electrically conductive layer (or second contact). Either the electron transporting layer or the hole transporting layer can be designed as the emissive layer and the light can be transmitted either way but generally exits through one of the conductive layers. There are many ways to modify one of the conductive layers for the emission of light therethrough but it has been found generally that the most efficient OED includes one conductive layer which is transparent to the light being emitted. Also, one of the most widely used conductive, transparent materials is indium-tin-oxide (ITO), which is generally deposited in a layer on a transparent substrate such as a glass plate.
Some major problems that are prevalent in prior art OEDs are caused by the interface between the electron transporting layer and the hole transporting layer. Generally, electron transporting organic material and hole transporting organic material are not compatible and do not easily bond together. One explanation for this is that electron transporting organic material is generally a hydrophilic material and hole transporting organic material is generally a hydrophobic material. This incompatibility results in a rough interface which has a strong tendency to separate under higher temperatures. Thus, the reliability of the OED is substantially reduced. Also, this rough interface may actually result in higher hole injection barriers (especially if partial separation occurs) in OEDs which utilize the electron transport layer as the emission layer.
Accordingly, it would be highly advantageous to provide a smooth reliable region between the electron transporting layer and the hole transporting layer.
It is a purpose of the present invention to provide a new and improved organic electroluminescent device.
It is another purpose of the present invention to provide a new and improved organic electroluminescent device with an improved region between an electron transporting region and a hole transporting region.
It is still another purpose of the present invention to provide a new and improved organic electroluminescent device with improved reliability and operation.
It is a further purpose of the present invention to provide a new and improved method of fabricating organic electroluminescent devices.
It is still a further purpose of the present invention to provide a new and improved method of fabricating organic electroluminescent devices with a smooth reliable region between an electron transporting region and a hole transporting region.